Lattice softening enables highly reversible sodium storage in anti-pulverization Bi–Sb alloy/carbon nanofibers

The high theoretical capacity of Sb-based intermetallic alloys makes them attractive potential anode materials for sodium-ion batteries (SIBs) with high energy density. However, their cycling stability is greatly restricted by the huge volumetric variations resulted from the intrinsic (de-)alloying mechanism. Herein, we demonstrate a unique lattice softening mechanism, which enables highly reversible sodium storage and stable cycling of the as-prepared Bi–Sb alloy/carbon nanofibers electrodes. Theoretical analyses show that the elastic modulus of Bi–Sb alloys is reduced whereas the toughness is enhanced by tuning the lattice chemistry of rhombohedral Bi–Sb alloys, which is of great importance in relieving the concentrated stress during the continuous (de-)sodiation processes. In-situ characterization and electrochemical evaluations demonstrate that the electrodes made of BiSb3/C nanofibers exhibit high anti-pulverization capability upon Na-cycling and extraordinary long-life cyclability. Specifically, a highly reversible capacity of 233.2 mAh g−1 at 2 A g−1 is achieved over 2500 cycles. Moreover, a full cell assembled with the pre-sodiated BiSb3/C anode and a Na3V2(PO4)3/C cathode delivers a high reversible capacity of 333.2 mAh g−1 at 0.2 A g−1 over 200 cycles. This present work provides further understandings and new solution for developing high-performance alloying-based anodes for SIBs.